Power amplification module

ABSTRACT

Provided is a power amplification module that includes: a first transistor, a first signal being inputted to a base thereof; a second transistor, the first signal being inputted to a base thereof and a collector thereof being connected to a collector of the first transistor; a first resistor, a first bias current being supplied to one end thereof and another end thereof being connected to the base of the first transistor; a second resistor, one end thereof being connected to the one end of the first resistor and another end thereof being connected to the base of the second transistor; and a third resistor, a second bias current being supplied to one end thereof and another end thereof being connected to the base of the second transistor.

CROSS REFERENCE TO RELATED APPLICATION

This is a Continuation of U.S. patent application Ser. No. 16/351,916filed on Mar. 13, 2019. The content of this application is incorporatedherein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to a power amplification module.

Description of the Related Art

A power amplification module is used in a mobile communication devicesuch as a cellular phone in order to amplify the power of a signal to betransmitted to a base station. In such a power amplification module, thegain may be switched in accordance with the output level in order toimprove the power addition efficiency. For example, in JapaneseUnexamined Patent Application Publication No. 2004-128704, aconfiguration is disclosed in which the gain is adjusted by changing thecurrent that flows to an amplifier of a power amplification module in apower amplification circuit formed of transistors that are connected inparallel with each other. In this configuration, variations in the inputimpedance that occur with a change in current are suppressed by acomplicated large-scale control circuit mounted on the bias circuit sideof the power amplification module.

However, there is a demerit in mounting a complicated large-scalecontrol circuit in a power amplification module in order to suppress thevariations in input impedance in that the chip area becomes larger. Onthe other hand, when the number of operating transistors is changed inorder to adjust the gain, the input impedance of the power amplificationcircuit changes. Consequently, the voltage standing wave ratio (VSWR) atthe input of the power amplification circuit may be degraded.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure was made in light of such circumstances and it isan object thereof to suppress a change in input impedance that occurswith a change in gain in a power amplification module that is capable ofchanging the gain thereof.

A power amplification module according to a preferred embodiment of thepresent disclosure includes: first transistor, a first signal beinginputted to a base thereof; a second transistor, the first signal beinginputted to a base thereof and a collector thereof being connected to acollector of the first transistor; a first resistor, a first biascurrent being supplied to one end thereof and another end thereof beingconnected to the base of the first transistor; a second resistor, oneend thereof being connected to the one end of the first resistor andanother end thereof being connected to the base of the secondtransistor; and a third resistor, a second bias current being suppliedto one end thereof and another end thereof being connected to the baseof the second transistor. At the time of a high gain mode, the firstbias current is supplied to the bases of the first and secondtransistors via the first and second resistors, respectively. At thetime of a low gain mode, the second bias current is supplied to the baseof the second transistor via the third resistor and is supplied to thebase of the first transistor via the third, second and first resistors,and a second signal, which is obtained by amplifying the first signal,is outputted from the collectors of the first and second transistors.

According to the preferred embodiment of the present disclosure, achange in input impedance that occurs with a change in gain can besuppressed in a power amplification module that is capable of changingthe gain thereof.

Other features, elements, characteristics and advantages of the presentdisclosure will become more apparent from the following detaileddescription of preferred embodiments of the present disclosure withreference to the attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates an example configuration of a transmission unit thatincludes a power amplification module according to an embodiment of thepresent disclosure;

FIG. 2 illustrates an example of the configuration of a poweramplification module;

FIG. 3 is a diagram for explaining the operation of the poweramplification module in the case of a high gain mode;

FIG. 4 is a diagram for explaining the operation of the poweramplification module in the case of a low gain mode;

FIG. 5 illustrates an example of the relationship between the number oftransistors and a change in gain; and

FIG. 6 illustrates an example of the relationship between the number oftransistors and the voltage standing wave ratio.

FIG. 7 illustrates an example of the configuration of a poweramplification module according to a second embodiment of the presentdisclosure.

FIG. 8 illustrates a graph of changes in gain in the power amplificationmodule of the second embodiment illustrated FIG. 7.

FIG. 9 illustrates a graph of changes in VSWR in the power amplificationmodule of the second embodiment illustrated FIG. 7.

FIG. 10 illustrates an example of the configuration of a poweramplification module according to a modification of the secondembodiment illustrated in FIG. 7.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereafter, an embodiment of the present disclosure will be describedwhile referring to the drawings. FIG. 1 illustrates an exampleconfiguration of a transmission unit that includes a power amplificationmodule according to an embodiment of the present disclosure. Atransmission unit 100 is for example used in a mobile communicationdevice such as a cellular phone in order to transmit various signalssuch as speech and data to a base station. Although such a mobilecommunication device would also be equipped with a reception unit forreceiving signals from the base station, the description of such areception unit is omitted here.

As illustrated in FIG. 1, the transmission unit 100 includes a modulator110, a power amplification module 120, a front end unit 130 and anantenna 140.

The modulator 110 modulates an input signal on the basis of a modulationscheme such as high speed uplink packet access (HSUPA) or long termevolution (LTE) and generates a radio frequency (RF) signal forperforming wireless transmission. The RF signal has a frequency ofaround several hundred MHz to several GHz, for example.

The power amplification module 120 amplifies the power of the RF signal(RF_(IN)) outputted from the modulator 110 up to the level that isrequired to transmit the RF signal to the base station, and outputs anamplified signal (RF_(OUT)). The power amplification module 120 operatesin a gain mode that corresponds to a gain mode control voltage V_(MODE).The gain mode may be a high gain mode or a low gain mode, for example.

The front end unit 130 filters the amplified signal and switches areception signal received from the base station. The amplified signaloutputted from the front end unit 130 is transmitted to the base stationvia the antenna 140.

FIG. 2 illustrates an example of the configuration of the poweramplification module 120. The power amplification module 120 includestransistors T1, T2, T3 and T4, capacitors C1, C2, C3, C4 and C5,resistors R11, R12, R13, R14, R23 and R24, an inductor L1, bias circuits200 and 210 and a bias control circuit 220.

The transistors T1 to T4 are amplification transistors and areheterojunction bipolar transistors (HBTs), for example. The transistorsT1 to T4 are connected in parallel with one another and form a singleamplification circuit. Each of the transistors T1 to T4 can serve as onefinger of a multi-finger transistor. The RF signal (RF_(IN)) is inputtedto the bases of the transistors T1 to T4 via the capacitors C1 to C4,respectively. In addition, a power supply voltage V_(CC) is supplied tothe collectors of the transistors T1 to T4 via the inductor L1. Thetransistors T1 to T4 output the amplified signal (RF_(OUT)) of the RFsignal (RF_(IN)) from their collectors via the capacitor C5.

A bias current I_(BIAS1) is supplied to one end of the resistor R11 andthe other end of the resistor R11 is connected to the base of thetransistor T1. The bias current I_(BIAS1) is supplied to one end of theresistor R12 and the other end of the resistor R12 is connected to thebase of the transistor T2. The bias current I_(BIAS1) is supplied to oneend of the resistor R13 and the other end of the resistor R13 isconnected to the base of the transistor T3. The bias current I_(BIAS1)is supplied to one end of the resistor R14 and the other end of theresistor R14 is connected to the base of the transistor T4. A biascurrent I_(BIAS2) is supplied to one end of the resistor R23 and theother end of the resistor R23 is connected to the base of the transistorT3. The bias current I_(BIAS2) is supplied to one end of the resistorR24 and the other end of the resistor R24 is connected to the base ofthe transistor T4.

The bias circuit 200 generates the bias current I_(BIAS1) on the basisof a bias control voltage V_(BIAS1). The bias circuit 200 includes atransistor T31, for example. The transistor T31 is an HBT, for example.The bias control voltage V_(BIAS1) is supplied to the base of thetransistor T31, the power supply voltage V_(CC) is supplied to thecollector of the transistor T31 and the emitter of the transistor T31 isconnected to one end of each of the resistors R11 to R14.

The bias circuit 210 generates the bias current I_(BIAS2) on the basisof a bias control voltage V_(BIAS2). The bias circuit 210 includes atransistor T32, for example. The transistor T32 is an HBT, for example.The bias control voltage V_(BIAS2) is supplied to the base of thetransistor T32, the power supply voltage V_(CC) is supplied to thecollector of the transistor T32 and the emitter of the transistor T32 isconnected to one end of each of the resistors R23 and R24.

The bias control circuit 220 controls the bias control voltagesV_(BIAS1) and V_(BIAS2) on the basis of the gain mode control voltageV_(MODE). Specifically, at the time of the high gain mode, the biascontrol circuit 220 makes the bias control voltage V_(BIAS1) be at ahigh level and the bias control voltage V_(BIAS2) be at a low level. Inaddition, at the time of the low gain mode, the bias control circuit 220makes the bias control voltage V_(BIAS2) be at the high level and thebias control voltage V_(BIAS1) be at the low level. The high level is avoltage that is higher than a threshold voltage at which the transistorsT31 and T32 that form the bias circuits 200 and 210 switch on and thelow level is a voltage that is lower than this threshold voltage.

Referring to FIGS. 3 and 4, an example of the operation of the poweramplification module 120 will be described.

FIG. 3 is a diagram for explaining the operation of the poweramplification module 120 in the case of the high gain mode. In the caseof the high gain mode, the bias control circuit 220 makes the biascontrol voltage V_(BIAS1) be at the high level and the bias controlvoltage V_(BIAS2) be at the low level. Thus, the transistor T31 of thebias circuit 200 is switched on and the transistor T32 of the biascircuit 210 is switched off. The bias current I_(BIAS1) is outputtedfrom the bias circuit 200.

The bias current I_(BIAS1) is supplied to the base of the transistor T1via the resistor R11. Similarly, the bias current I_(BIAS1) is suppliedto the bases of the transistors T2 to T4 via the resistors R12 to R14,respectively. Thus, the transistors T1 to T4 are switched on and the RFsignal (RF_(IN)) is amplified by the transistors T1 to T4.

FIG. 4 is a diagram for explaining the operation of the poweramplification module 120 in the case of the low gain mode. In the caseof the low gain mode, the bias control circuit 220 makes the biascontrol voltage V_(BIAS1) be at the low level and the bias controlvoltage V_(BIAS2) be at the high level. Thus, the transistor T31 of thebias circuit 200 is switched off and the transistor T32 of the biascircuit 210 is switched on. The bias current I_(BIAS2) is outputted fromthe bias circuit 210.

The bias current I_(BIAS2) is supplied to the base of the transistor T3via the resistor R23. Similarly, the bias current I_(BIAS2) is suppliedto the base of the transistor T4 via the resistor R24. Thus, thetransistors T3 and T4 are switched on.

The bias current I_(BIAS2) is supplied to the base of the transistor T1via the resistors R23, R13 and R11. Similarly, the bias currentI_(BIAS2) is supplied to the base of the transistor T2 via the resistorsR23, R13 and R12. In addition, the bias current I_(BIAS2) is supplied tothe base of the transistor T1 via the resistors R24, R14 and R11. Inaddition, the bias current I_(BIAS2) is supplied to the base of thetransistor T2 via the resistors R24, R14 and R12. However, the amount ofthe current supplied to the bases of the transistors T1 and T2 is smallcompared with the amount of the current supplied to the transistors T3and T4. Consequently, although the transistors T1 and T2 are notentirely switched off, the size of the emitter current per unit emitterarea is small compared with that for the transistors T3 and T4.Therefore, the gain generated by the transistors T1 to T4 is smallerthan that in the case of the high gain mode illustrated in FIG. 3.

As described with reference to FIGS. 3 and 4, in the power amplificationmodule 120, the transistors T1 to T4 are switched on by the bias currentI_(BIAS1) being supplied to the bases of the transistors T1 to T4 in thecase of the high gain mode. In addition, in the case of the low gainmode, the bias current I_(BIAS2) is supplied to the bases of thetransistors T3 and T4 and the transistors T3 and T4 are switched on.Furthermore, the bias current I_(BIAS2) is also supplied to the bases ofthe transistors T1 and T2 via the resistors R13 and R14 and thetransistors T1 and T2 enter a state of not being completely switchedoff.

In the power amplification module 120, the gain can be made to changethrough this type of operation. In the power amplification module 120,since the transistors T1 and T2 are not completely switched off in thecase of the low gain mode, the change in the input impedance can besuppressed compared with the case where the transistors T1 and T2 arecompletely switched off.

In the power amplification module 120, the number of transistors thatform the amplification circuit is four, but the number is not limited tothis. Furthermore, in the power amplification module 120, the number oftransistors for which the size of the supplied bias current becomessmall at the time of the low gain mode is two (transistors T1 and T2),but the number is not limited to this. For example, the number oftransistors for which the size of the supplied bias current becomessmall at the time of the low gain mode may be three (for example,transistors T1 to T3) or one (for example, transistor T1).

Referring to FIGS. 5 and 6, the characteristics of the poweramplification module 120 will be described.

FIG. 5 illustrates an example of the relationship between the number oftransistors and the change in gain. The horizontal axis represents thenumber of transistors that are completely switched on and the verticalaxis represents the change in gain, with a state in which the number oftransistors that are directly contributing to amplification (that arecompletely switched on) is four serving as a reference.

In FIG. 5, the solid line represents an example of the simulationresults for the same configuration as that of the power amplificationmodule 120 of this embodiment (configuration in which a current is alsosupplied to transistors that do not directly contribute toamplification). In addition, the broken line represents an example ofthe simulation results for a typical configuration in which a current isnot supplied to transistors that do not directly contribute toamplification. As illustrated in FIG. 5, in the same configuration asthat of the power amplification module 120, the gain can be reduced bydecreasing the number of transistors that directly contribute toamplification (are completely switched on) at the time of the low gainmode.

FIG. 6 illustrates an example of the relationship between the number oftransistors and the voltage standing wave ratio. The horizontal axisrepresents the number of transistors that are completely switched on andthe vertical axis represents the voltage standing wave ratio at theinput of the power amplification module (input VSWR).

In FIG. 6, the solid line represents an example of the simulationresults for the same configuration as that of the power amplificationmodule 120 (configuration in which a current is also supplied totransistors that do not directly contribute to amplification). Inaddition, the broken line represents an example of the simulationresults for a typical configuration in which a current is not suppliedto transistors that do not directly contribute to amplification. Asillustrated in FIG. 6, in the same configuration as that of the poweramplification module 120, since there are transistors that are notcompletely switched off at the time of the low gain mode, the change ininput impedance is suppressed and as a result the degradation of theinput VSWR can be suppressed.

An exemplary embodiment of the present disclosure has been describedabove. According to the power amplification module 120, the transistorsT1 and T2 are not completely switched off at the time of the low gainmode. Consequently, a change in the input impedance that occurs with achange in the gain can be suppressed in the power amplification module120.

Although the power amplification module 120 is a single-stageamplification circuit, the present disclosure can be similarly appliedto an amplification circuit having two or more stages. In the case wherethe present disclosure is applied to an amplification circuit having twoor more stages, the same configuration may be adopted in all of thestages or the same configuration may be adopted in only some of thestages.

FIG. 7 illustrates a power amplifier 120B according to a secondembodiment of the present disclosure. Description of points that arecommon to this embodiment and FIG. 2 and description of similarconfigurations are omitted. In the configuration illustrated in FIG. 7,only resistors R11 and R12 are connected to the emitter of thetransistor T31. In other words, relative to the configurationillustrated in FIG. 2, the resistor R13 and the resistor R14 have beenremoved in the configuration illustrated in FIG. 7. In the case of thisconfiguration, in a high power mode operation (a high gain mode), biascontrol voltages V_(BIAS1) and V_(BIAS2) are respectively supplied tothe bases of the transistor T31 and the transistor T32, and biascurrents I_(BIAS1) and I_(BIAS2) are supplied from the respectiveemitters of the transistor T31 and the transistor T32 to the bases ofthe transistors T1 to T45 via the resistors R11, R12, R23, and R24. Inan ideal state, the bias control voltages V_(BIAS1) and V_(BIAS2) wouldhave identical values and the bias currents I_(BIAS1) and I_(BIAS2)would also have identical values and be equal to Icurrent1. However,there will be a certain difference due to processing variations, butthese parameters should still have substantially identical values. Onthe other hand, when operating in a low power mode (a low gain mode),the input impedances of the transistors T1 to T4 seen from RF_(IN)change by a large amount compared with at the time of the high powermode due to the transistors T3 and T4 being completely turned off.Therefore, to prevent input of an RF signal from being obstructed to anincrease in VSWR, when operating in the low power mode, a bias controlvoltage V_(BIAS1) is supplied to the base of the transistor T31 from thebias control circuit 220. A bias control voltage V_(BIAS2) is suppliedto the base of the transistor T32 from the bias control circuit 220. Abias control voltage V_(BIAS2) is a lower voltage than a bias controlV_(BIAS1). As a result, a bias current I_(BIAS2) (Current 3), which issmaller than the bias current I_(BIAS1) (Current 2) that flows to theemitter of the transistor T31, flows to the emitter of the transistorT32. Since the current I_(BIAS2) is smaller than the current I_(BIAS1),the transistor T3 and the transistor T4 can be switched to a state thatis not completely switched off.

As a result of being switched to this state, as illustrated in FIGS. 5and 6, changes in VSWR can be suppressed while providing a difference ingain. In this configuration, the transistors T1 to T4 are switched on atthe time of the high power mode, and in the low power mode it isnecessary for the transistors T3 and T4 to be not completely switchedoff while the transistors T1 and T2 are switched on. The configurationillustrated in FIG. 7 involves more complex control compared with theconfiguration illustrated in FIG. 2. The values of the currents at thetime of the high power mode and the low power mode are illustrated inTable 1, where Current1>Current2>Current 3.

Here, in order to find the appropriate value of Current 3, a simulationwas performed in order to check the changes in gain and VSWR that occurwhen the bias current I_(BIAS1) is constant and the bias currentI_(BIAS2) is varied. The simulation was based on four drive stagetransistors with two transistors driven by each of the transistor T31and by the transistor T32.

FIG. 8 illustrates a graph of changes in gain where the horizontal axisrepresents a ratio between the bias current I_(BIAS2) that flows to theemitter of the transistor T32 and the bias current I_(BIAS1) that flowsto the emitter of the transistor T31. When the value of the bias currentI_(BIAS2) is identical to that of the current I_(BIAS1) (Current 2), thegain is 16.5 dB. When the current I_(BIAS2) does not flow (i.e., 0.0%),the gain is 13.6 dB. It is clear that the gain changes in asubstantially linear manner as the bias current I_(BIAS2) changes.

FIG. 9 illustrates a graph of changes in VSWR where the horizontal axisrepresents a ratio between the bias current I_(BIAS2) that flows to theemitter of the transistor T32 and the bias current I_(BIAS1) that flowsto the emitter of the transistor T31. As is clear from the figure, it isclear that VSWR is 2 in the case where the bias current I_(BIAS2) doesnot flow (i.e., 0.0%) and that the value of VSWR approaches 1.4 as thevalue of the bias current I_(BIAS2) approaches the value of the biascurrent I_(BIAS1). However, in contrast to the changes in gainillustrated in FIG. 8, VSWR does not change linearly. In particular, asthe bias current I_(BIAS2) approaches 0, VSWR changes sharply.Therefore, from the viewpoint of changes in the VSWR characteristic andgain, the gain is less than 16.5 and VSWR is less than 1.8 in a range inwhich the bias current I_(BIAS2) is between 20% and 80% of the currentI_(BIAS1). Therefore, when operating in the low power mode, a suitablerange for Current 3 is from 20% to 80% of Current 2.

TABLE 1 Sizes of emitter currents of transistor T31 and transistor T32in second and third embodiments. I_(BIAS1) I_(BIAS2) High Power ModeCurrent 1 Current 1 (High Gain Mode) Low Power Mode Current 2 Current 3(Low Gain Mode)

FIG. 10 illustrates a power amplifier 120C according to a modificationof the second embodiment illustrated in FIG. 7. The configurationillustrated in FIG. 10 differs from the configuration illustrated inFIG. 7 in that the bias control circuit 220 is replaced with a biascontrol circuit 220B that is a current-control-type bias control circuitthat supplies currents Icontrol1 and Icontrol2 to the bases of thetransistor T31 and the transistor T32. Due to this configuration, thesensitivity with which the emitter currents of the transistor T31 andthe transistor T32 can be adjusted is low compared with thevoltage-control-type configuration, and therefore control is easier.Therefore, it is possible to more finely control adjustment of VSWR andadjustment of gain at the time of the low power mode. The values of thebias currents I_(BIAS1) and I_(BIAS2) are hfe (current amplificationfactor) times as large as the values of the currents that flow to thebases of the transistors T31 and T32, and therefore there is aproportional relationship between the currents Icontrol1 and Icontrol2.Therefore, it may be said that the value of the current Icontrol2 whenoperating in the low power mode suitably lies between 20% and 80% of thecurrent Icontrol1.

The purpose of the embodiments described above is to enable easyunderstanding of the present disclosure and the embodiments are not tobe interpreted as limiting the present disclosure. The presentdisclosure can be modified or improved without departing from the gistof the disclosure and equivalents to the present disclosure are alsoincluded in the present invention. In other words, appropriate designmodifications made to the embodiments by one skilled in the art areincluded in the scope of the present disclosure so long as themodifications have the characteristics of the present disclosure. Forexample, the elements included in the embodiments and the arrangements,materials, conditions, shapes, sizes and so forth of the elements arenot limited to those exemplified in the embodiments and can beappropriately changed. In addition, the elements included in theembodiments can be combined as much as technically possible and suchcombined elements are also included in the scope of the presentdisclosure so long as the combined elements have the characteristics ofthe present disclosure.

While preferred embodiments of the disclosure have been described above,it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the disclosure. The scope of the disclosure, therefore, isto be determined solely by the following claims.

What is claimed is:
 1. A power amplification module comprising: a firsttransistor, a first signal being inputted to a base of the firsttransistor; a second transistor, the first signal being inputted to abase of the second transistor and a collector of the second transistorbeing connected to a collector of the first transistor; a thirdtransistor, the first signal being inputted to a base of the thirdtransistor, and a collector of the third transistor being connected tothe collector of the second transistor; a first resistor, a first biascurrent being supplied to a first end of the first resistor and a secondend of the first resistor being connected to the base of the firsttransistor; a second resistor, a first end of the second resistor beingconnected to the first end of the first resistor, and a second end ofthe second resistor being connected to the base of the secondtransistor; and a third resistor, a second bias current being suppliedto a first end of the third resistor and a second end of the thirdresistor being connected to the base of the third transistor, wherein:when the power amplification module operates in a first mode, the firstbias current is supplied to the base of the first transistor via thefirst resistor and to the base of the second transistor via the secondresistor, and the second bias current is supplied to the base of thethird transistor via the third resistor, when the power amplificationmodule operates in a second mode the first bias current is supplied tothe base of the first transistor via the first resistor and to the baseof the second transistor via the second resistor, and the second biascurrent is supplied to the base of the third transistor via the thirdresistor, and when the power amplification module operates in the secondmode, the second bias current has a non-zero value that is less than avalue of the first bias current.
 2. The Power amplification moduleaccording to claim 1, further comprising: a fourth transistor, the firstsignal being inputted to a base of the fourth transistor and a collectorof the fourth transistor being connected to a collector of the firsttransistor; and a fourth resistor, a first end of the fourth resistorbeing connected to the first end of the third resistor and a second endof the fourth resistor being connected to the base of the fourthtransistor.
 3. The Power amplification module according to claim 1,wherein the value of the second bias current is between 20% and 80% ofthe value of the first bias current.
 4. The Power amplification moduleaccording to claim 2, wherein the value of the second bias current isbetween 20% and 80% of the value of the first bias current.
 5. The Poweramplification module according to claim 1, further comprising: a biascontrol circuit configured to control the value of the second biascurrent and to control the value of the first bias current, wherein thebias control circuit is a current-control-type bias control circuit. 6.The Power amplification module according to claim 2, further comprising:a bias control circuit configured to control the value of the secondbias current and to control the value of the first bias current, whereinthe bias control circuit is a current-control-type bias control circuit.7. The Power amplification module according to claim 3, furthercomprising: a bias control circuit configured to control the value ofthe second bias current and to control the value of the first biascurrent, wherein the bias control circuit is a current-control-type biascontrol circuit.
 8. The Power amplification module according to claim 4,further comprising: a bias control circuit configured to control thevalue of the second bias current and to control the value of the firstbias current, wherein the bias control circuit is a current-control-typebias control circuit.